Method and an apparatus for continuously deaerating a liquid

ABSTRACT

The invention relates to a method for continuously deaerating a liquid. The method comprises the step that the liquid is led into a closed container ( 1 ) so that a liquid surface ( 7 ) is formed within the container ( 1 ). The space above the liquid surface ( 7 ) is under vacuum. The method further includes the step that a gas is led into the liquid at a level below the liquid surface ( 7 ). The invention also relates to an apparatus which comprises a closed container ( 1 ). The container ( 1 ) has an inlet ( 5 ) for the liquid which is to be deaerated, as well as an outlet ( 6 ) for the liquid which has been deaerated, both placed in the lower region of the container ( 1 ). The container ( 1 ) further has a connection ( 13 ) to a vacuum pump ( 14 ) placed in the upper region of the container ( 1 ), as well as an inlet ( 15 ) for a gas placed in the lower region of the container ( 1 ).

FIELD OF THE INVENTION

The present invention relates to a method for continuously deaerating,or purging, a liquid which is led into a closed container so that aliquid surface is formed within the container.

The present invention also relates to an apparatus for continuouslydeaerating a liquid, comprising a closed container, with an inlet and anoutlet for the liquid located in the lower region of the container.

BACKGROUND OF THE INVENTION

All liquids contain more or less air in free, dispersed or dissolvedform. Within the industry which employs process water, there is often aneed to remove this air. Above all within the food industry, this isoften necessary, since a content of air may result in the deteriorationof the quality of the product, or alternatively hamper those processesthat are being employed.

For example, in the production of fruit juices or beverages containingfruit juices, it is particularly important, since oxygen oxidizes theproduct and destroys the important vitamin C. Too large a content of airis also a disadvantage as regards the production of carbonated drinks,since it makes it more difficult to add carbon dioxide. Milk-basedproducts are also deaerated, since a large content of air results in adeterioration in quality and disrupts the process in that scorching ofthe product, so-called fouling in heat treatment plants increases withan increased air content. An excessively large air content may alsocause frothing in certain processes, which is difficult to handle.

There are a number of methods and apparatuses employed in the art forremoving air from liquids. A common method entails that the liquid, at acertain temperature, is distributed in a vacuum vessel. The pressure inthe vessel is kept at such a level that a certain degree of boilingoccurs, so-called flash. The alternative to flash is that the vacuumvessel is filled with a packing material through which the liquid iscaused to pass, but without the occurrence of boiling. This method maybe speeded up by introducing, under partial vacuum, a gas such as carbondioxide into the liquid, and by such means drive out and replace the airwith the gas. This method is often entitled stripping and isparticularly suitable for liquids which are later to be carbonated.

The methods in existence today often function satisfactorily but entailthat there is a need to invest in special equipment. In certain cases,such equipment may also be extremely bulky.

SUMMARY OF THE INVENTION

One object of the present invention is to realise a method forcontinuously deaerating a liquid which is simple and economical andwhich gives an efficient deaeration.

A further object of the present invention is that the apparatus forcarrying the method into effect is economical and may rapidly beintegrated or retrofitted into a process line without taking up a largeamount of space.

These and other objects have been attained according to the presentinvention in that the method of the type disclosed by way ofintroduction has been given the characterising features that the spaceabove the liquid surface is under vacuum, and that a gas introduced intothe liquid at a level below the liquid surface.

These and other objects have also been attained according to the presentinvention in that the apparatus of the type disclosed by way ofintroduction has been given the characterising feature that thecontainer, in its upper region, has a connection to a vacuum pump, andthat the container has, in its lower region, an inlet for a gas.

Preferred embodiments of the present invention have further been giventhe characterising features as set forth in the appended subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

One preferred embodiment of the present invention will now be describedin greater detail hereinbelow, with reference to the accompanyingDrawings, in which:

FIG. 1 is a schematic illustration of an apparatus according to a firstembodiment of the present invention.

FIG. 2 is a schematic illustration of an apparatus according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus, as shown in FIG. 1, comprises a closed container 1. Inthis first preferred embodiment, the container 1 is in the form of aninverted U with two shanks 2, 3. The shanks 2 and 3 are united by acommon web portion 4. The common web portion 4 constitutes the upperregion of the container 1.

In the lower region of the container 1, placed in the one shank 2, thereis an inlet 5 for the liquid to be deaerated. In the second shank 3, inthe lower region of the container 1, there is provided an outlet 6 forthe liquid which has been deaerated. The liquid passes through thecontainer 1 in such a manner that a liquid surface 7 is formed in thecommon web portion 4 in the upper region of the container 1. In order tofacilitate the passage of the liquid through the container 1, apressurising pump 8 may be placed in a conduit 9 upstream of the inlet 5to the container 1. This pump 8 is, however, not necessary for carryingthe method into effect. In order to move the deaerated liquid whichdeparts from the container 1 further, a pressurising pump 10 may beplaced in a conduit 11 downstream of the outlet 6 from the container 1.

The container 1 may very simply be manufactured from pipes and pipebends. The inlet 5 and the outlet 6 are connected to the container 1 bymeans of conical pipe lengths (not shown). By employing this simpledesign of the container, no costly vacuum vessels are necessary forcarrying the method into effect. Nor will the container 1 in thisembodiment be particularly bulky and it may readily be integrated orretrofitted into an existing conduit.

In that a liquid surface 7 is formed in the upper region of thecontainer 1, there will be created a space 12. This space 12 isconnected by the intermediary of a conduit 13 to a vacuum pump 14. Thevacuum pump 14 creates low pressure, or alternatively a vacuum (0–0.2bar) in the space 12 above the liquid surface 7.

In addition to an inlet for liquid which is to be deaerated, the oneshank 2 also has an inlet 15 for a gas. The inlet 15 for gas is providedwith some form of throttle valve 16. Further, in direct association withthe gas inlet 15, there is a bubble-generating device 17. The device 17may consist of an extremely fine-meshed net or a metal plate in whichextremely small holes are provided. Alternatively, the device 17consists of a diaphragm- or a microfilter.

The second preferred embodiment is shown in FIG. 2. The apparatuscomprises the closed container 1 in the form of an inverted U with twoshanks 2, 3. The shanks 2 and 3 arc united by the common web portion 4constituting the upper region of the container 1.

In the lower region of the container 1, placed in the one shank 2, thereis an inlet 5 for the liquid to be deaerated. In the second shank 3, inthe lower region of the container 1, there is provided an outlet 6 forthe liquid which has been deaerated. The liquid passes through thecontainer 1 in such a manner that a liquid surface 7 is formed in thecommon web portion 4 in the upper region of the container 1. In order tofacilitate the passage of the liquid through the container 1, apressurising pump 8 may be placed in the conduit 9 upstream of the inlet5 to the container 1. This pump 8 is, however, not necessary forcarrying the method into effect.

In order to move the deaerated liquid which departs from the container 1further, a pressurising pump 10 is to be placed in the conduit 11downstream of the outlet 6 from the container 1. Between the outlet 6and the inlet 5 in the container there is a circulation pipe 18,arranged so that the pressurising pump is used to circulate the liquidover the container 1. The conduit 11 is also to contain some sort ofthrottle valve 19 located downstream of the circulation pipe 18.

As in the first embodiment of the invention, in this second embodiment,the container 1 may very simply be manufactured from pipes and pipebends. The inlet 5 and the outlet 6 are connected to the container 1 bymeans of conical pipe lengths (not shown). By employing this simpledesign of the container, no costly vacuum vessels are necessary forcarrying the method into effect. Nor will the container 1 in thisembodiment be particularly bulky and it may readily be integrated orretrofitted into an existing conduit.

In that a liquid surface 7 is formed in the upper region of thecontainer 1, there will be created a space 12. This space 12 isconnected by the intermediary of a conduit 13 to a vacuum pump 14. Thevacuum pump 14 creates low pressure, or alternatively a vacuum (0–0.2bar) in the space 12 above the liquid surface 7.

In addition to an inlet for liquid which is to be deaerated, the oneshank 2 also has an inlet 15 for a gas. The inlet 15 for gas is providedwith some form of throttle valve 16. Further, in direct association withthe gas inlet 15, there is a bubble-generating device 17. The device 17may consist of an extremely fine-meshed net or a metal plate in whichextremely small holes are provided. Alternatively, the device 17consists of a diaphragm- or a microfilter.

The liquid which is to be deaerated preferably consists of water whichmay thereafter be diluted with juice concentrate or the like, dependingupon what process the water is to be employed for. Other liquids such asfruit juices, fruit drinks or milk, may also be deaerated employing thismethod.

The gas which is employed in the method according to the presentinvention preferably consists of air at atmospheric pressure. Since thedeaeration is intended for food products, the air should be of very highquality and must, if necessary be cleaned before being employed in themethod. Alternatively, other gases such as nitrogen gas or carbondioxide may also be employed. If the liquid is, later in the process, tobe carbonated, carbon dioxide may be employed as the gas, but if not,use is suitably made of air, nitrogen or other suitable gas.

The method is carried into effect in that the liquid which is to bedeaerated is led into the closed container 1. At the same time as theliquid enters into the container 1, a gas flows into the container 1through the bubble-generating device 17. The bubble-generating device 17divides the gas into a large number of extremely small bubbles. Thesmall bubbles form “cores” for the air which is in the liquid in free,dispersed or dissolved form. The “cores” grow to larger air bubbleswhich, when they are sufficiently large, move up towards the liquidsurface 7. The air leaves the liquid and the container 1 through theconduit 13.

No great pressure need be applied on the liquid which is entering thecontainer 1. However, the pressure should be higher than the pressureprevailing above the liquid surface 7. The pressure above the liquidsurface 7 lies at vacuum or very close to vacuum. Nor does the gas whichis fed into the container 1 need to be pressurised. However, thepressure within the container 1 should be lower in order to make itpossible for the gas to enter into the container 1.

According to the first embodiment of the invention the deaerated liquidis leaving the container 1 via the outlet 6 and is transported furtheralong the conduit 11, possibly helped with the pressurising pump 10.

According to the second embodiment of the invention, the liquid leavingthe container 1 at the outlet 6 is circulated over the circulation pipe18, back to the inlet 5 of the container 1. In order to improve thedeaeration of the liquid, the liquid is circulated 3 to 5 times over thecontainer 1, before it is transported further along the conduit 11. Thecontainer 1 with the inlet 5, the outlet 6, the circulation pipe 18, thepressurising pump 10 and the throttle valve 19 thereby constitute a feedand bleed arrangement.

The above-described method and the apparatus for carrying the methodinto effect make for an efficient deaeration which meets thoserequirements placed by the processing industry for the production ofdrinks and the like. For example, for juice production, an oxygencontent applies of 1 ppm or lower.

As will have been apparent from the foregoing description, the presentinvention realises a method for continuously deaerating a liquid whichis efficient and economical to carry out, since air may be employed asthe gas which constitutes the “cores” in the method. The apparatus forcarrying the method into effect is also simple and economical tomanufacture and it may readily be integrated or retrofitted into anexisting plant.

1. A method of continuously deaerating a liquid to remove gas from theliquid, comprising leading the liquid into a closed container so that aliquid surface is formed within the container, introducing gas into theliquid at a level below the liquid surface, and creating a vacuum in aspace above the liquid surface to draw off the gas that has been removedfrom the liquid, and wherein the gas that is introduced into the liquidat a level below the liquid surface and the gas that is removed from theliquid and drawn off are the same, and the gas introduced into theliquid at a level below the liquid surface is air.
 2. The method asclaimed in claim 1, wherein the air introduced into the liquid at alevel below the liquid surface is air at atmospheric pressure.
 3. Themethod as claimed in claim 1, wherein the air introduced into the liquidat a level below the liquid surface passes a bubble-generating deviceupon inflow of the air to the liquid.
 4. The method as claimed in claim3, wherein the bubble-generating device divides the air into a largenumber of small bubbles which constitute “cores” for the air which theliquid contains.
 5. The method as claimed in claim 1, wherein the liquidis circulated over the container.
 6. The method as claimed in claim 5,wherein the liquid is circulated 3 to 5 times.
 7. An apparatus forcontinuously deaerating a liquid, comprising a closed container, with aninlet and an outlet for the liquid, located in the lower region of thecontainer, wherein the container has, in its upper region, a connectionto a vacuum pump and wherein the container has, in its lower region, aninlet for a gas, wherein the container is in the form of an inverted Uwith the inlet for the liquid in a first shank and the outlet for theliquid in a second shank, and wherein the inlet for the gas is placedclose to the inlet for the liquid.